Process and system for the production and purification of helium

ABSTRACT

An overall process comprising a series of three successive operations for deriving helium from natural gas and purifying it to 99.9969 mol percent, minimum. In the initial operation, the natural gas feed, containing 15 to 40 mol percent of helium, is cooled and flashed in two stages. Both the crude helium product and the vaporized condensate from the flash stages serve to refrigerate the feed stream. The condensate by-product provides commercial grade fuel gas. In the intermediate operation, an input stream having a helium content from 60 to 80 mol percent is enriched to a purity of 85 to 97 mol percent by cooling it to below liquid nitrogen temperature, and passing it through a helium separator. The effluent helium-rich vapor is optionally reheated, then work expanded, and used as a refrigerant for the feed stream. Dissolved helium is removed from the condensate in the helium separator by auxiliary flashing, and returned to the recycle stream, the condensate from the latter stage ultimately serving as a refrigerant. In the final operation, the enriched helium undergoes purification by catalytic action to remove hydrogen. It is then dried, compressed, cooled, passed through several stages of flashing and additional cooling, and through carbon adsorbers to remove the balance of nitrogen. The cold, nearly pure product is finally heat exchanged with a feed stream prior to storage. Condensate from the flashing stages, and liquid from an auxiliary nitrogen system provide refrigeration for the final purification operation.

United States Patent [191 Lofredo et al.

[ June 11, 1974 [75] Inventors: Antony Lofredo, Springfield; Alfred J. Surowiec, Maplewood, both of NJ.

[73] Assignee: Airco, Inc., New York, NY.

[22] Filed: July 31, 1969 [21] Appl. No.: 846,490

[52] U.S. Cl 62/22, 62/14, 62/39, 62/18, 62/24 [51] Int. Cl. FZSj 3/00, F25j 3/06, F25j 5/00 [58] Field of Search 23/1 E, 4; 62/9, 11, 22, 62/23, 24, 27, 28, 39, 51, l4, 18; 423/659 [56] References Cited UNITED STATES PATENTS 2,576,985 12/1951 Wildhack ..62/51 2,582,885 l/1952 Rosenblatt.... 23/4 3,123,981 3/1964 Carney 62/51 3,130,027 4/1964 Harper 62/23 3,148,966 9/1964 Kitchen..... 62/23 3,205,669 9/1965 Grossmann 62/28 3,240,023 3/1966 DeLano 62/23 3,254,496 6/1966 Roche 62/23 3,260,058 7/1966 Ray 62/23 3,293,869 12/1966 Karbosky 62/23 3,331,213 7/1967 Harmens 62/23 3,407,614 10/1968 Poska 62/23 3,415,069 12/1968 Hauser 62/22 3,440,829 4/1969 Davies-White... 62/51 3,512,368 5/1970 Harper 62/23 3,653,220 4/1972 Foster 62/23 FOREIGN PATENTS OR APPLICATIONS 488,100 12/1952 Canada 23/1 E BATTERY LlMllTS N G DOME CRUDE SEPARATION UNIT ntuun rum ncmon as L 4c FIGS.

Primary Examiner-Norman Yudkoff Assistant ExaminerA. Purcell Attorney, Agent, or Firm-Edmund W. Bopp; H. Hume Mathews; Roger M. Rathbun [5 7] ABSTRACT An overall process comprising a series of three successive operations for deriving helium from natural gas and purifying it to 99.9969 mol percent, minimum. In the initial operation, the natural gas feed, containing to mol percent of helium, is cooled and flashed in two stages. Both the crude helium product and the vaporized condensate from the flash stages serve to refrigerate the feed stream. The condensate byproduct provides commercial grade fuel gas. In the intermediate operation, an input stream having a helium content from to mol percent is enriched to a purity of to 97 mol percent by cooling it to below liquid nitrogen temperature, and passing it through a helium separator. The effluent helium-rich vapor is optionally reheated, then work expanded, and used as a refrigerant for the feed stream. Dissolved helium is removed from the condensate in the helium separator by auxiliary flashing, and returned to the recycle stream, the condensate from the latter stage ultimately serving as a refrigerant. In the final operation, the enriched helium undergoes purification by catalytic action to remove hydrogen. It is then dried, compressed, cooled, passed through several stages of flashing and additional cooling, and through carbon adsorbers to remove the balance of nitrogen. The cold, nearly pure product is finally heat exchanged with a feed stream prior to storage. Condensate from the flashing stages, and liquid from an auxiliary nitrogen system provide refrigeration for the final purification operation.

44 Claims, 12 Drawing Figures NELIUM S ORAGE PAIENTEDJIIII I I I974 3.815.876 SHEET F 9 FIG./

46 BATTERY 6 LIMITS 5 FUEL b GAS SYSTEM I00 A I 2 3 LIQUID 7 DISPOSAL N.G. ,4 CRUDE SEPARATION CRUDE 9 II DOME V UNIT HELIUM Lfi (FIG. 2) I M23 [3 a (V) jI 1 I 2% coNsERvATIoN LINE I o ATMOSPHERE b{I4 HELIUM E N ICRINC I Ag v ALTERNATIVE FIGS 19 V I8 3A & 3B(CONNECTED 2| /22 [6 44 27 28 AS 3C),3D&3E I 1 CRUDE G6 V I24 I5 a N2 29 SYSTEM 400 600 36 g HELIUM 2 A STORAGE HELIUM as 3 PuRIFICATIoN' 37 4' 2 v uNIT GAS TO FROM I 32 FIGS.4A,4B&4C ATMOSPHERE FUEL GAS (CONNECTED As 40) J SYSTEM) FUELGAS WASTE 4a 31 N2 INVENTORS A'LOFREDO A .J. S UROW/E C A T TOR/V5 I PATENTEDJUNH m4 1815376 SHEET 8 BF 9 A 7' TOR/ 5. V

PROCESS AND SYSTEM FOR THE PRODUCTION AND PURIFICATION OF HELIUM BACKGROUND OF THE INVENTION This relates in general to the purification and processing of low boiling gases, and more particularly, to a process comprising a series of operations for producing highly purified helium, together with commercial by-products, from natural gas.

Helium has many applications in modern technology, the most important of which arch the aircraft and missile industry, where it is used to pressurize missile and rocket propellant tanks. An important metallurgical use of helium is in the shielded-arc welding of metals, and in plasma-jet torches used for cutting. In addition, it has many refrigeration applications, such as providing low temperature environments for certain types of masers and lasers, and also for superconductor systems. Other important commercial applications are in providing a controlled inert atmosphere for growing germanium and silicon crystals, for cooling vacuum fur naces, and in processing fuel elements for nuclear reactors. Helium is also used in many laboratory and research operations.

These many present-day applications require substantial amounts of helium, which in most cases must be of a high grade of purity, substantially free of contaminants. Although small amounts of helium are present in the earths crust, and atmosphere, the most important source is in natural gas. Inasmuch as the helium would ordinarily be lost if not extracted before the gas burns, it is important that it be separated from natural gas before the latter is consumed and marketed. Therefore, it is important to provide highly economical separation processes of high thermodynamical efficiency in which the losses of helium are minimized. It is also important that the residue gas from the helium separation process be available as fuel, and at temperatures and pressures suitable for piping in a natural gas system.

It is, accordingly, the principal object of this invention to improve the processing of low boiling gases, more particularly helium.

A more specific object is to provide more efficient production of high purity helium with the simultaneous production of refrigerants and fuel by-products in usable commercial form.

BRIEF DESCRIPTION OF THE INVENTION These and other objects are attained in accordance with the present invention in a three-part system, each of whose units may be used as separate entities without the other two, or combined as a single integrated system. The first unit effects a crude separation of helium to between 60 and 80 mol per cent purity from a natural gas feed source. The second unit may use the output of the first, or the output of an independent source, or a combination from several sources, to produce an enriched helium product purified to between about 85 and 97 mol percent. The third unit may use the enriched product from the second unit, or from an independent source, to produce a final helium product of Grade A purity in which the contaminants are reduced to as low as three parts per million.

The process in the first unit produces crude helium from natural gas by a series of steps which comprise cooling the feed gas by heat exchange with the product and residue streams, separating out condensed hydrocarbons, subcooling the remaining feed gas, stripping the feed gas of helium by flashing in a plurality of stages, deriving the crude helium product as vapor from the primary helium stripping stage, recycling the partially-helium vapor derived from the secondary helium stripping and flashing stages, and vaporizing the condensate so obtained to provide refrigeration'for the process.

The process carried out in the intermediate unit enriches the crude helium stream having an initial pressure of about atmospheres and a temperature of between about 45 and F, by cooling it to below liquid nitrogen temperature, and using a helium separator to separate out the helium-enriched vapor product, which is returned, through the system, after a workexpansion step, to cool the feed stream. The liquid condensate from the helium separator is passed through one or more stages of flashing to remove dissolved helium vapor, which, together with other vapor components, including nitrogen, is returned through the systerm for recycling. Both the streams returned for recycling and the liquid condensate are used for refrigerating the feed streams. In a preferred embodiment, the enriched helium vapor passes through a reheat step to eliminate liquid, prior to work expansion in a turboexpander. In accordance with another feature, the liquid condensate from the flashing stages may be distilled in a reboiler in a heat exchange with a small component of partially liquefied feed stream to derive additional dissolved helium. In another embodiment, a subcooler is interposed between the feed gas heat exchanger and the helium separator.

In the process in thefinal unit, the helium-rich feed stream may be derived from the enriching unit, or from an independent source, at about 60 atmospheres pressure. This is passed through a platinum catalyst in the presence of air for the removal of all but a slight excess of hydrogen, which is removed subsequently in a copper oxide bed. The stream is dried, further compressed to about 186 atmospheres, and further cooled, after which it is passed through three stages of flashing with intervening cooling in heat exchangers, two of which include boiling nitrogen. The resultant helium vapor containing less than 1 mol percent nitrogen is passed through a low temperature, high pressure carbon adsorber which functions to remove the balance of the nitrogen from the helium stream. The nearly 100 percent pure product stream is then heat exchanged with feed streams, before passing to storage. Part of the refrigeration for the system is derived from the streams of liquid condensate flowing out of the flashing stages; whereas, the refrigeration for the carbon adsorber and nitrogen boilers is fumished by an off-site source of compressed nitrogen gas which is liquefied in an ancillary system. Nitrogen for the off-site source may be derived from condensate from flashing stages in earlier parts of the system which has been appropriately processed.

The principal advantage of the systems of the present invention is that they provide for the production of a helium product of 99.9969 minimum mol percent purity by processes of improved thermal efficiency, in which the need for external refrigeration is minimized, and in which the hydrocarbon by-product gases are of commercial quality.

Other objects, features, and advantages of the system of the present invention will be apparent to those skilled in the art after a study of the detailed specification hereinafter with reference to the attached drawings.

SHORT DESCRIPTION OF THE DRAWINGS FIGS. 3A and 3B, combined as indicated in block diagram 3C, form a detailed showing in schematic diagram of the preferred embodiment of a helium enriching unit corresponding to block 200 in FIG. 1 of the drawings;

FIG. 3D is a detailed showing of an alternative form of the helium enriching unit shown in block 200 of FIG.

FIG. 3B is a modification of the helium enriching unit shown in FIG. 3D;

FIGS. 4A, 4B, and 4C, combined as shown in diagram 4D, form a detailed showing in schematic of the final helium purification unit corresponding to block 400 in the block diagram of FIG. I; and

FIG. 4E is a detailed showing of one of the carbon a sorbers of FIG. 4C.

Referring to FIG. 1 of the drawings, there-is shown in a compilation of block diagrams, an overall system in accordance with the present invention, including a crude separation unit 100, a helium enrichment unit 200, and a helium purification unit 400. Each of these units shown in block diagram will be described in substantial detail hereinafter. It will be noted that cooling water and instrument air lines have been omitted for simplification.

Unit 100 is retained in an insulated cold box 10, the outer walls of which comprise a carbon-steel structure, having dimensions 9.5 feet by 9.5 feet by 30 feet. The space between vessels is filled with a heat insulating material, such as inorganic wool, the space being maintained by means of nitrogen gas at a pressure slightly above barometric pressure, for exampleat a pressure of about 5 inches of water.

Helium enriching unit 200 and helium final purification unit 400 can either be insulated separately in in structures of the general form of cold box 10, or the two units 200 and 400 can be enclosed in spaced-apart relation in a single overall cold box 20. The space between the walls of box 20 is also maintained at a pressure of about 5 inches of water,-above barometric pressure.

The system shown in block 100 is indicated in detail in a preferred embodiment shown in FIG. 2 of .the drawings. Unit 200 is shown in alternative configurations in the detailed diagrams of FIGS. 3A, 38 combined as FIG. 3C, and in FIGS. 3D and 3E of the drawings. Unit 400 is shown in detail in FIGS. 4A, 4B, and 4C, combined as FIG. 4D of the drawings.

Crude gas fed from the source 1, which may be, for example, an underground natural gas dome, is piped through a 6-inch conduit under control of the valve 3, into the crude separation unit 100. The feed gas enters the unit through conduit 2 at a pressure of about 30 atmospheres and at a temperature of 80F. This input stream comprises natural gas containing between and 40 mol percent of helium.

After processing the natural gas feed in the crude separation unit 100, in a manner to be described in detail hereinafter, a residue of processed fuel gas, which is methane-rich gas from which the helium has been removed, passes off through a 10-inch diameter conduit 4 under control of the valve 5, at a pressure of about 5 atmospheres, and at a temperature between about 65 and F. This stream has a heat rating of between 896 and 960 British Thermal Units per cubic feet, depending on the composition of the natural gas input. The stream is forced by centrifugal pump 6 to pass to fuel gas storage system 46. Liquid disposal from the water coolers in the unit 100 flows ofi through the conduit 7. The crude helium output, which is 60 to mol percent pure, flows through the 6-inch diameter conduit 8 at a pressure of about 30 atmospheres and at a temperature of 65F, through the normally open valve 9, from which it is forcedby the compressor 1 1 through a conduit system leading into the conservation pipeline 12a for storage at about 80 atmospheres.

A feed stream from the conservation pipeline 12a passes through the 6-inch diameter conduit 13 under control of valve 14, from which it passes into the helium'enrichment unit 200. The latter can assume any one of the forms indicated in FIGS. 3A and 38, combined as 3C, FIG. 3D or FIG. 3B. The stream through conduit 13 enters at the storage pressure of about 80 atmospheres and at a temperature of between 45 and 100F. This feed stream consists of between about 60 and 80 mol percent helium, with a balance of additional components including hydrogen, nitrogen, and methane.

After the processing in one of the three alternative enrichment units 200, a residue gas comprising waste nitrogen, including a small percentage of methane, either passes back into the system for recycling, or flows out through the conduit 17 at atmospheric pressure and at a temperature between 19 and 30F, under control of the valve 18, flowing at a flow-rate depending on the nitrogen in the input stream and the specific enrichment process, and passes off into the atmosphere or for other application, as explained hereinafter. The enriched product, which is now between and 97 mol percent helium, depending on the composition of the input stream and the exact process used, includes as impurity small amounts of hydrogen and nitrogen. It flows out at a pressure of about 58 atmospheres and at a temperature somewhere between 19 and l00F, depending on the specific one of the alternative processes used, through the 4-inch diameter conduit 19 to the junction 21. At this point part of the flow may be returned, at the above pressure, by opening valve 30 leading through the 4-inch diameter conduit 22 to the conservation pipeline 12b, where it is maintained or stored at a pressure of approximately 59 atmospheres at ambient temperature.

The balance of the stream passes through the 4-inch diameter conduit 24 to the junction 25. An additional or alternative input stream of crude gas from a source 44, alternative to the crude separation unit 100 or one of the helium enriching units 200, may be directed through conduit 26, under the force of pump 27 and under control of the valve 28. For example, this may comprise a stream of 87.7 mol percent helium with a balance of nitrogen and hydrogen impurity, flowing at a pressure of about 59 atmospheres or a little less and at a temperature a little above ambient. The combined stream from the junction 25 flows through the 4-inch diameter conduit 29, serving as input to the helium purification unit 400. The merged input flow has an initial temperature of about 80F and an input pressure of about 58 atmospheres. In the examples under descrip- 5 .which is controlled by valve 32, and which serves as fuel for preheat of the copper oxide beds for the reduction of hydrogen, as will be explained in detail hereinafter. In addition, a stream of nitrogen from an off-site source 45 passes at a pressure of about 41 atmospheres and at a temperature of 90F, through the normally open valve 34, into the purification unit 400 to function as a refrigerant in the process. The fuel gas supply 48 may be derived from fuel gas system 46; and the nitrogen supply for source 45 may be derived from appropriately processed condensate from unit 400, as will be described hereinafter.

After the final purification process has taken place in the unit 400, which is described in detail hereinafter with reference to FIG. 4 of the drawings, Grade A product helium, having a minimum purity of 99.9969

mol percent, passes out through the l-inch diameterconduit 35 under control of valve 36, at a pressure of about 180 atmospheres and at a temperature of about 90F, to storage 600, pending loading in vessels or tanks for transportation to the points for use.

A stream of methane-rich nitrogen passes out of the system at about atmospheric pressure and at a temperature of 80F through the normally open valve 38. Waste nitrogen, returning from the system at about atmospheric pressure and at a temperature of about 85F, passes out through the 4-inch diameter conduit 41, through the valve 42, and into the atmosphere, or alternatively, through valve 49, and conduit 51 to the nitrogen storage system 45 for reprocessing.

The several units which are components of the overall purification and enrichment system will now be described individually in detail. Each unit will be described, for the purposes of illustration, with reference to the processing of one or more input streams of preselected composition which in each case enters the unit at a stated pressure, temperature, and flow rate. However, it will be understood that the units describedare not limited to the processing of feed streams of the specific characteristics recited by way of example.

The crude helium separation unit 100 is shown in detail in FIG. 2 of the drawings. Operation of unit 100 will be described with reference to two illustrative feed streams having the following characteristics.

Table l-Continued Feed Stream The Flow Rates indicated in Table 1 above, and in the text and tables hereinafter are computed at F at a presure of one atmosphere.

In this system a feed gas having the general composition and flow rate indicated in Table l, flows in at a pressure of 463 pounds per square inch absolute and a temperature of F, through the conduit 2 to the junction 101, where it merges with the stream returning for recycle. The combined stream flows from junction 101 through the conduit 102 to the column 103a of the fivecolumn heat exchanger 103, which may be of a brazed aluminum plate-and-fin type, where it is cooled to below 140F by a heat exchange with the product and residue streams passing out through the other four columns.

The cooled stream then flows through the conduit 104 to the inlet 105 of the first stage 106a of the flash drum 106. The latter is a conventional cylindrical flash vessel of stainless steel or the like, 10 to 12 feet tall and about 2 feet in diameter, bowed outwardly at the top and bottom ends, and having two compartments of about equal height, superposed vertically. The vessel 1060 is designed to have approximately a 2 minute residence time. At the top of vessel 106a is interposed a demister 108, comprising a pancake-shaped wire mesh 6 inches thick, for removing entrained liquid from the rising vapor. The pressure in the first-stage flash drum 106a is maintained at 447.7 pounds per square inch absolute, and the temperature at -l47.8F in Case A and 143F in Case B, so that the low boiling gases, including helium, nitrogen, and some methane, rise to the top, whereas most of the heavy hydrocarbons become liquefied and fall to the bottom of the vessel. Leading out from the dome of the first-stage flash drum 106a is a conduit through which the low boiling helium-rich vapor passes out. This vapor has the composition and flow rate indicated in the following Table 2.

Table 2 Flash Gas From Flash Drum 1060 Case A Case B Flow Rate (Std. Cubic FtJMin.) [at 70F, 1 atm. pressure] 9,699 10,358 Composition (Mol Helium 17.82 36.54 Nitrogen 28.29 28.62 Methane 52.74 33.49 Ethane 1.09 1.21 Propane 0.05 0.13 Butane 0.01 0.01

the vapor stream is further cooled to a temperature of 257.8F in Case A, and 253.3F in Case B, by countercurrent heat exchange with the streams of returning condensate, helium product, and helium bearing vapor returning for recycle. The cooled helium-rich stream then passes through the conduit 117 to the inlet pipe 118 of the first stage 119a of helium stripper 119.

The helium stripper 119, which is a stainless steel cylindrical vessel 23 feet high and 32 inches in diameter, is separated vertically into three substantially equal length compartments, the first stage 119a at the bottom, the second stage 1 19b in the middle, and the third stage 1196 at the top. At the top of each stage is interposed a de-mister comprising a stainless steel wire mesh 4 inches thick, which serves to entrap liquid passing up with the vapor through the top stage.

The bottom stage 119a is maintained at an internal pressure of about 446 pounds per square inch, absolute, and at a temperature of 257.8F, in case A, and 253.3F, in case B. The partial-liquid entering through inlet pipe 118 is flashed in vessel 119a. The residue, which includes primarily nitrogen and methane, sinks to the bottom of the vessel; while the vapor phase, consisting of about 60 mol percent helium, rises to the top of this stage. The vapor then passes upward and out through the conduit 143, leading from the top of the lower stage of helium stripper 119 at a temperature of 257.8F, in case A, and 253.3F, in case B, and a pressure of 445.68 pounds per square inch,-absolute. This crudely purified product stream, comprising about 63 mol percent of helium, passes from conduit 143 to the passage c of the heat exchanger 116, where it is warmed up to a temperature of l90F, in case A, and 168 F, in case B, in a heat exchange with the stream being cooled. The warmed crude-product stream then passes out of heat exchanger 116 through the conduit 144 and into passage b of the feed gas heat exchanger l03. ln the latter, the stream is warmed up to a temperature of 69F, in case A, and 72F, in case B; and passes out of the unit 100 at a pressure of 440 pounds per square inch,.absolute for storage in the conservation pipeline 12a of F 1G. 1, from which it may either be transported for immediate use, or piped to helium enriching unit 200 for further purification. The

flow rate and composition analysis of the crude product stream is shown in Table 3 below.

Returning now to the auxiliary systems, the liquid condensate, comprising primarily the heavy hydrocarbons, which collects in the bottom of the first-stage flash drum 106a, flows off through pipe 111 through valve 112, at a pressure of 447.7 pounds per square inch, absolute. Valve 112 is pneumatically controlled by a liquid level device 112a in a manner well-known in the art, to maintain the liquid in the bottom of the flash vessel at a preselected level. The temperature,

flow rate, and composition of the condensate are given in the following Table 4.

Table 4 Liquid Condensate First-Stage Flash Drum The hydrocarbon liquid stream passes through valve 112 and conduit 113 to the second-stage flash drum 10612, which is maintained at an internal pressure of about 197.68 pounds per square inch, absolute. Methane-rich liquid forms in the bottom of this vessel, the vapor, including some dissolved helium, rising to the top of the second-stage 10612 and passing out through the conduit 109 at a pressure of 197.68 pounds per square inch, absolute. The temperature, flow rate, and composition of this partial helium stream are given below in Table 5.

Table 5 Vapor Second-Stage Flash Drum Case A Case B Temperature (F) 169.5 149.6 Flow Rate (Std. cubic ftjmin.) [at F, 1 atm. pressure] 198 33 Composition (Mol Helium 1.42 4.43 Nitrogen 28.95 39.70 Methane 68.58 54.25 Ethane 1.02 1.49 Propane 0.04 0. l 3

This partially helium vapor stream passes into the passage 0 of heat exchanger 103 where it is warmed up to a temperature of 69F, in case A, and 72F, in case B, passing out through the conduit and into the junction 139, at which point it is joined by a partially helium stream returning from the helium stripper, as will be described hereinafter. The pressure of this returning recycle stream is retained at a preselected value by means of valve 153 connected to the feed stream, which is operated pneumatically by the pressureresponsive device 153a when the pressure in conduit 110 becomes low.

The methane-rich liquid condensate in the secondstage flash drum 106b passes out through conduit 114 to junction 147, under control of valve 148, which is operated pneumatically by the liquid level control de-' vice 148a to maintain the liquid in the vessel at a predetermined level. This liquid stream has a temperature and composition indicated in Table 6, below.

Table 6 Methane-Rich Condensate Second-Stage Flash Drum The liquid passes into the upper stage 1190 of the helium stripper through intake 125. The temperature, flow rate, and composition of this condensate are given in Table 9 below.

Case A Case B Temperature (F) l69.5 l49.6 Table 9 Flow Rate (Std. cubic ftJmin.) g g zg g Ls g 3: gzi 040 293 Condensate Second-Stage Helium Stripper Case A Case B 35* M030 0018 Temperature ("F) 25s.4 254.l

ltrogen 3241 3'456 10 Flow Rate (Std cubic ft /min Methane 48.327 26.908 0 Eth 22 874 21 167 [at 70 F, 1 atmos. pressure] 6952 4334 Millie 141572 271515 (Md Butane 10.978 20.936 Helium 0072 (L072 Nitrtggen 26.761 24.776 Me ane 71.571 71.948

From unction 147, this methane-rich stream passes 2-377 to column e of heat exchanger 103, either alone, or merged wlth a stream of llquld condensate from helium As in the Stage below, the heliumqich vapor rises to stripper 119, as will be descr1bed heremafter.

. the top of stage 119c and passes out through demlster Returnlng now to helium stripper 119, llquld conden- 1226' and conduit 132 at a pressure of 80 pounds per sate, lncludlng nitrogen and methane, collects in the square inch absolute, the temperature, flow rate, and bottom of the lowest stage 119a. Th1s liquid 15 drawn com Sition bein in Table 10 beow off through conduit 145 under control of the valve 124, p0 g g] which is pneumatically (or electrically) regulated to Table 10 keep the level of the liquid in the lowest stage 119a at a preselected level. This stream passes off at a pressure apor Third-Stage Helium Stripper of 445.7 pounds per square inch absolute. Its tempera- Case A Case B ture, flow rate, and composition are given in Table 7, Temperature (F) 264.4 26l.l below. Flow Rate (Std. cubic ft./min.)

[at 70F, 1 atm. pressure] 280 202 Table 7 3O Composition (Mol Helium 1.740 1.53 Condensate First-Stage Helium Stripper Ni 'ogen 84.080 82.15'

Case A Case B T "F 257.8 -253.3 Fi o w a t e i stii. dubic ftJmin.) The liquid collected In the bottom of the thlrd-stage 3} z gessufel 6994 4366 vessel 1190 passes off through the conduit 123 under control of valve 150 and pneumatic liquid level device Helium 0.286 0.316 150a, at a pressure of 80 pounds per square inch, abso- N'tro en 26.907 24.986 Mlelhgne 71.219 7;.518 40 1gb; giniilpelrzgliei 1flow rate, and composltlon are Ethane 1.513 .856 P 0.068 0.299 0:35:2 0.007 0.025 Table 11 I Liquid Third-Stage Helium Stripper The stream drawn through the valve 124 passes into C A C B the second stage 1191) of the stripper through conduit Temperature "1: 3 521 120. Th1s vessel is mamtamed at an internal pressure of Flow l lale (Std. cubic ftJmin.)

197.7 pounds per square inch absolute. The process is gg zg g x z ngffzfi 4132 again repeated with the vapor, including dissolved he- Helium 0.002 0.001 llum, rlslngto the top of the second stage vessel 1191 Nitrogen 24.355 21.978 and the major portion of the condensate, Including n1- Methane 73980 74661 trogen and methane, becoming liquefied in the bottom. Ethane 1.585 3.017

. Propane 0.071 0.316 Butane 0.007 0.027

The vapor from this stage rlses through the demlster 122b, and passes out through the outlet-l26.

The stream in conduit 126 passes out through the The stream flowing from the conduit 123 passes back valve 151 to the junction 133, where it is joined by a throughthe column a of heat exchanger-116 where it stream from the third stage 119v of the helium stripper is heated upto a temperature of l90F in case A and 3 from conduit 132. Valve 151 is controlled by a pneul67F in case B, in a heat'exchange with the cooling matically actuated control device 151a which responds liquids. Conduit 146 leads out from column a of heat to the pressure in line 126. Vessel 119v ismaintained exchanger 116 to the junctionl55. at an internal pressure of pounds per square inch ab- In accordance with one alternative, valve 157 is solute. closed and the methane-rich stream passes through The stream of liquid from stage; 11% passes out from open valve 156 to passage f of heat exchanger 103, the bottom through conduit 128 at a pressure of 65 where it is heated up to a temperature of 69F and 72F pounds per square inch gauge, through valve 129, which is pneumatically controlled by a liquid level device 129a to maintain the liquid level in vessel 11%.

in cases A and B, respectively. ,This stream-then flows through conduit 158 to junction 160.1f valve 161 is open and valve 162 is closed, the stream flows through conduit 163 to junction 164, where it joins the recycle stream through compressor 137; If valve 161 is closed and 162 is open, the stream flows to junction 169 where it joins the stream through valve 167, as will be described, being pumped to fuel gas system 46 for use commercially, or in other units of the purification system.

Assuming valve 157 to be closed, the stream of liquid condensate which has passed out of conduit 114 in flash vessel 106b, passes through valve 148 and moves as a separate stream into conduit 149 and column e of heat exchanger 103, in which it is heated up to 69F, in case A, and 72F in case B. It subsequently passes through conduit 159 to junction 165 where, assuming valve 167 to be closed and valve 166 to be open, it passes through conduit 168 to junction 164 to join the recycle through the system. Assuming valve 167 to be open and valve 166 to be closed, the methane-rich stream passes into junction 169 where it merges with the stream from valve 162, the merged stream passing out through conduit 4, as previously described. Such a system provides flexibility in control of the volume and composition of the recycle stream. The increased recycle stream obtained in this manner supplies additional refrigeration through joule-thompson expansion after compression.

Assuming valve 156 to be closed and valve 157 to be open, the two methane-rich streams merge at junction 147 ahead of heat exchanger 103, the merged stream passing through column e, conduit 159, through open valve 167, and to outlet conduit 4 through junction 169. This merged stream of residue gas, which passes through outlet 4 at a pressure of 73 poundsper square inch, absolute, has the following temperature, flow rate, heat capacity, and approximate analysis, as indicated in Table 12, below.

. This gas, which is suitable for fuel, is passed to fuel gas system 46 of FIG. 1.

Returning now to the helium stripper, the partially helium vapor streams coming out the tops of the second and third stages 11% and 119: which are ,combined at junction 133, pass as a combined stream through the conduit 134, being warmed up to l90F, in case A, and to -1 68F, in case B, in column b of heat exchanger 1 16. The stream then returns through conduit 135 and column d of heat exchanger 103 where it is warmed up to 69F, in case A, and 72F, in case B, passing out through the conduit 136. At this point the stream has a pressure of 75 pounds per square inch, absolute. The pressure in this line is maintained at a preselected value by the pressure controlled valve 152, which connects this line to the feed stream 102. The

temperature, flow rate, and composition are given in Table 13.

Table 13 Recycle from Helium Stripper As previously described, this recycle stream may be merged with one or both, in whole or in part, of the hydrocarbon streams from conduits 158 and 159. The recycle stream passes into the compressor 137 where the pressure is raised to 190 pounds per square inch, absolute. The compressor 137 may be of any of the types well-known for helium separation systems. (See page 122 et. seq., Technology of Liquid Helium, National Bureau of Standards, Monograph, 1968). The compressor 137 is followed by a water-cooled after cooler 138, which compensates for the heat generated during the compression. The combined streams from the junc tion 139 pass through the conduit 140, where the merged stream is again compressed in the compressor 130, of. similar type to 137, passing out of the latter through the conduit 141 and through the after cooler 142, for further cooling. The returning, recycled stream, at this point, has a temperature of 100F and a pressure of 463 pounds per square inch, absolute. The temperature, flow rate, and analysis are shown in Table 14.

Table 14 Combined Recycle Case A Case 8 Temperature (T) 100 I00 Flow Rate (Std. Cubic i'L/min.) {at F, 1 atm. pressure] 520' 567 Composition (Mo! 56) Helium 4.37 5.70 Nitrogen 60.42 73.37 Methane 34.81 20.72 Ethane 0.39 0.19 Propane 0.01 0.02

the form of any of the systems indicated in FIGS. 3C,

3D or 3B of the drawings.

Let us refer, now, to the system shown in FIGS. 3A,

3B, assembled as shown in FIG. 3C, which is preferred for the purposes of the present invention. The crude helium stream passes in through the conduit '13 at a pressure of 1,213 pounds per square inch gauge. The temperature, flow rate, and composition are given in Table 15, below.

Table Feed Stream Preferred Enriching Unit This stream initially passes through a filter 201 comprising, for example, sintered stainless steel for removing any entrapped solids. The flow into the system is under control of a conventional cryogenic valve 206, electronically or pneumatically controlled by a pressure control system 206a which may be any one of the types well-known in the art. The incoming feed stream flows into the junction 207 where it is joined by the recycled stream 283, returning through a circuit which will be described in detail hereinafter.

The combined feed and recycle stream in conduit 208 flows at a pressure of 1,213 pounds per square inch, absolute. The temperature, flow rate, and compo sition are given below in Table 16.

This combined stream passes into the junction 209, at which point between about 1 and 2 percent by volume flows through the arm 211 and the remaining major portion, flows into the arm 212. The conduit 212 passes into the conventional wound-tube type heat exchanger 213 through the coil 213a where it is cooled down to a temperature slightly below 316F. The stream, having substantially the same analysis as previously indicated, then flows into the temperature controlled valve 215. The latter is electronically or pneu matically controlled by a temperature-difi'erential indicating circuit 215a, which is connected between the outlet 257 of the heat exchanger 213 and outlet 260 of heat exchanger 217, and which responds to maintain the temperature differentials across the heat exchangers 213 and 217 substantially constant. The valve 215 is a three-way valve having, in addition to the lead-in from the conduit 214, a lead-in for the minor component through conduit 266. This minor component stream is derived from a path which passes through the conduit 21] through the passage 217a of heat exchanger 217, where it is separately cooled down to between 264F and 28 1F (depending on the composition of the input), through conduit 264, reboiler coil 265, returning through conduit 266 to the left-arm of the three-way valve 215. The reboiler coil 265 serves to further cool the minor component in a heat ex- 315.7F, the flow rate and composition being indicated below in Table 17.

Table 17 Enriched Product Stream Case A Case B Flow Rate (Std. Cubic ftJmin.) [at 70F, 1 atm. pressure] 10,364 12,015 Composition (Mol Hydrogen 1.7276 1.1902 Helium 95.6954 96.2061 Nitrogen 2.5571 2.5896 Methane 0.0199 0.0141

change with evaporating condensate in helium stripper 259, as will be further described hereinafter.

The streams combine at the output of valve 215 to form a single stream which passes through the conduit 222 at a pressure of 1,181 and 1,184 pounds per square inch, absolute, in cases A and B, respectively, and at a temperature of 3l5 .7F, the flow rate and composition being indicated in the foregoing Table 16.

The conduit 222 passes to the intake 223 of the helium separator 224. The latter is a conventional flash vessel maintained at an internal pressure of about 1 181 and 1184 pounds per square inch absolute, in Cases A and B, respectively. This vessel comprises, for example, stainless steel 1% feet in diameter and 9 feet high, having a de-mister 225, which comprises a disc of wire mesh, say 6 inches thick. The enriched helium vapor rises to the top of this vessel, the higher boiling components, including most of the nitrogen, which have become liquefied, falling to the sump where they collect. The liquid level in the sump is maintained constant by means of the output valve 229, connected to the conduit 228 at the bottom of the vessel. Valve 229 is either electronically or pneumatically controlled by a liquidlevel control circuit 229a, most likely taking the form of a differential pressure sensing element.

The vapor output from the dome of the vessel 224 passes out through the conduit 226 at a pressure of 1181 and 1184 pounds per square inch, absolute, in cases A and B, respectively, and at a temperature of This helium-enriched product stream passes into the junction 231. Assuming temperature-regulated control valve 234 to be closed, the entire stream passes through conduit 232 to junction 237 at the intake of the turboexpander 239. If the probe from the electronic or pneumatic temperature-regulating circuit 234a, which is interposedin the expander intake stream, indicates that the stream is likely to be below the condensation point after turbo-expansion, valve 234 is opened to allow part of the stream to pass through conduit 235 to the outer channel 213d of the wound-tube heat exchanger 213, where it undergoes a reheat step, being warmed up from 315.7F to 33F and 99F, in cases A and B, respectively. The reheated stream flows at pressures of 1,180 and 1,183 pounds per square inch, absolute in cases A and B, respectively, back into the main stream in conduit 232, where it serves to maintain the stream at a preselected temperature.

The temperature-controlled stream flows into the conventional turbine expansion device 239, where it is expanded with the performance of work to a pressure of about 875 pounds per square inch, absolute, being thereby cooled to a temperature of just below -319F. The function of the reheat step is to prevent the formation of a liquid phase as the stream passes into the turbo-expansion device, thereby reducing the errosive effeet on the latter. The expansion operation may, in some embodiments, serve to supply energy to other parts 'of the system, including the compressor stages 276 and 278 of the circuit with which the expander may be connected for tandem operation, in a manner well-known in the art.

After work-expansion, the cooled low-pressure stream returns through the inner tube 2l3b of heat exchanger 213 where it is heated up to a temperature of 33F, in case A and 94F in case B, passing into the conduit 242 and through the flow-regulated valve 247. The latter is operated under control of conventional electronic or pneumatic means 247a to regulate the flow into the output channel 19 in accordance with a predetermined flow rate. The stream flows out from the channel 19 at a pressure of about 863 pounds per square inch, absolute, the temperature, flow rate, and composition being given below in Table 18.

Table 18 Enriched Product Output Case A Case B Temperature (F1 33 94 Flow Rate (Std. cubic ftJmin.) (at 70F, 1 atm. pressure] 10,364 12,015 Composition (M01 Hydrogen 1.7276 1.1902 Helium 95.6954 96.2061 Nitrogen 2.5571 2.5896 Methane 0.0199 0.0141

Returning now to the helium stripper 224, the liquid settling in the bottom, as previously indicated, passes out through the vent 228 and the valve 229 which is electronically or pneumatically regulated by liquid level control circuit 229a, to keep a preselected liquid level in vessel 224. The liquid stream passes to the intake 248 of the helium flash drum 249, serving as a degaser, which is maintained at an internal pressure of about 30.0 pounds per square inch, absolute. The liquid in this entering stream flows into the vessel 249 at a pressure of about 1,181 or 1,184 pounds per square inch, absolute, in cases A and B, respectively, the temperature and flow rate being given in Table 19, below.

Table 19 Liquid Condensate from Helium Separator- Methane Case A Case B Flow Rate (Std. Cubic ftJmin.) [at 70F, 1 atm. pressure] 5,130 3,389 Composition (M01 16) Hydrogen 1.2253 0.8438 Helium 1.2143 1.2211 Nitrogen 94.7107 95.91 12 16 I The vapor rising through the de-mister 251 passes out through'the conduit 252 in the dome at a pressure of about 30 pounds per square inch, absolute. The temperature, flow rate, and composition of this vapor are given in Table 20, below.

Table 20 Vapor from Helium Flash Drum responsive to changes in the pressure and liquid level in the flash drum 249. Output from the valve 253 passes into the junction 268 where it may be joined by additional amounts of vapor including trace amounts of hydrogen and helium derived from the conduit 267 out of the helium stripper 259, in the case of vapor rising out of that vessel, as the result of reboiler action, as will be described. The returning stream, at a pressure of 20 pounds per square inch, absolute, in case A, flows at a temperature of 325.2F and at the rate of 216 standard cubic feet per minute; whereas, in case B, the temperature is 324.8F and the flow rate, 126 standard cubic feet per minute. This stream passes through the conduit 269 and into the outer channel 2l7b of heat exchanger 217 where it absorbs heat from the incoming feed stream, being thereby warmed up to a temperature of 33F, in case A, and 94F in case B, as it passes into the junction 260. i

The liquid passing out of the bottom of the helium flash drum 249 through conduit 255 typically flows at a pressure of 30 pounds per square inch, absolute. The temperature, flow rate, and composition are given in 1 Table 21 below.

Table 21 Liquid from Bottom Helium Flash Drum Case A Case B Temperature (F) 325.2 -324.8 Flow Rate (Std. Cubic fL/min.)

[at F, 1 atm. pressure] 4914 3263 Composition (Mol Hydrogen 0.2736 0.2060 Helium 0.0056 0.0066 Nitrogen 96.7468 97.6856 Methane 2.9740 2.1018

This stream passes through the inlet 258 where it is introduced into the helium stripper reboiler 259 at a point just below the wire mesh de-mister 261. The he lium stripper 259 is a cylindrical stainless steel vessel with bowed ends, 6 feet high and 1% feet in diameter. The wire mesh de-mister 261, which is 4 inches thick, is located on the top. The mid-section of the vessel is filled with stainless steel packing, such as shown, for example, in the following reference: Office of Scientific Research & Development, Rept. 3768, June 13, 1944, Liquid Air Fractionation.

In the bottom of the vessel 259, coil 265 is connected between conduits 264 and 266. The liquid from conduit 258 flows into the helium stripper-reboiler 259, where the internal pressure is maintained at about 20 pounds per square inch absolute. Liquid settling in the bottom of the vessel 259 is boiled in a heat exchange with the small component of feed gas passing through coil 265, cooling the latter and causing any remnants of helium to rise to the top of the vessel. Liquit mixed with any rising vapor is entrained in the wire de-mister 261, above. The liquid which settles in the bottom passes off through conduit 240, which is connected to a siphon arrangement 243. The latter, is U-shaped, so that the inverted closed end protrudes physically above the horizontal plane coinciding with the liquid level in vessel 259, providing a head which keeps the liquid in the vessel at a desired level. The closed top end of siphon 243 is connected through a pipe 244 which leads to normally open valve 245, leading to junction 246. Valve 245 may be manually adjusted to control the pressure differential across helium stripper 259, and to allow it to be emptied.

The liquid which typically passes off through conduit 240 at a reduced pressure of 20 pounds per square inch, absolute, has the same temperature and composition as indicated in Table 21 above, except that, depending on the composition of feed from input conduit 258, additional amounts of dissolved helium and hydrogen may pass out of conduit 267 and through junction 268 to conduit 269.

The liquid stream of the composition described in Table 21 flows out through conduit 250, through the inner tube 2130 of heat exchanger 213, where it is warmed up to 33F in case A, and 94F in case B, at a pressure near atmospheric, thereby cooling down the feed streams through heat exchange. This waste stream comprising mostly nitrogen then passes out through conduit 17 and to the atmosphere through vent 17a, or alternatively, for use in parts of the final helium purification system 400, in a manner set forth hereinafter. in

accordance with a further alternative, the nitrogen from conduit 17 is passed through valve 17b open for the purpose, and conduit 230, to join conduit 271 for compression with the recycle stream.

At the junction 260, the stream from the helium flash drum 249, including any trace amounts from the helium stripper 259, or any amounts of waste nitrogen from conduit 230, passes into conduit 271 to junction 272 at a pressure slightly above atmospheric pressure and at a temperature of 33F in case A, and 94F in case B, the composition of this stream being substantially that given in Table 20 above.

At the junction 272, the gaseous stream flows into the conduit 275 to compressor 276 where it is compressed from a pressure slightly above atmospheric pressure to a pressure of 1213 pounds per square inch, absolute. The stream passes out of compressor 276 and through the compressor aftercooler 278, which is water cooled to compensate for the heat of compression. The compressed stream passes through the conduit 279 to the separator 281, which comprises a flash drum, where any liquid, such as trace amounts of water, passes out through a drain 285, in the bottom. The remaining gas passes out through a vent at the top of separator 281 and into the junction 282. This stream, which has a pressure of 1213 pounds per square inch, absolute and a temperature of 100F, has a composition substantially the same as that given in Table 20 above. This stream then flows back into the junction 207 where it joins the feed system for recycling through the system. A small component may be returned through the conduit 284 and the valve 274, which is controlled by the pressure-sensitive circuit 274a interposed in the conduit 271. The function of this device is to keep the pressure in the conduit 271 at a preselected level.

Alternative to the helium enrichment circuit of unit 200 just described are the modified arrangements for helium enrichment shown in FIGS. 3D and 3E of the drawings.

Referring in detail to FIG. 3D, a crudely purified helium feed stream flows into the unit through the conduit 13 at a pressure of about 1,205 pounds per square inch, absolute. The temperature, flow rate, and composition, for alternative cases, are given in Table 22, below.

Table 22 Feed Stream First Alternate Enrichment Unit Case A Case B Temperature (F) 45 [00 Flow Rate (Std. Cubic fL/min.) [at F, 1 atm. pressure] l5,278 l5,278 Composition (Mol Hydrogen 1.26 0.98 Helium 64.92 75.66 Nitrogen 32.85 22.90 Methane 0.97 0.46

This feed system flows into the junction 210 where it is united with a recycle stream, the combined stream then flowing into column b of heat exchanger 287 where it is cooled down in each case to a temperature of -3l5.7F by counterflowing waste and product streams. This combined, cooled stream has approxi- After being cooled, it flows into the intake 289 to the helium flash drum 290. The latter is a cylindrical stainless steel drum with bowed ends, 9 feet high and 1% feet in diameter, which is maintained at an internal pressure of about atmospheres. At the top of the dome, there is interposed a wire mesh de-mister 291 which is 6 inches thick.

As in previously described flash drums, the vapor rises to the top, passing through the de-mister wire mesh 291 and out through the conduit 292 at a pressure of about 1,200 pounds per square inch, absolute,

and. at a temperature of 3 l 5.7-F. The entrapped liquid flows down to the bottom of the drum, where it passes out through the conduit 301. Y

19 The vapor stream which passes into junction 293 has a flow-rate and composition indicated in Table 24, below.

Table 24 Flash Drum Vapor Assuming valve 2930 to be closed, this stream passes into conduit 294 and through column a of heat exchanger 287.where it is warmed up to 308.7F at the intake to the expander 298.Assuming that the valve 2930 is open, all or a portion of the stream from junction 293 may be taken directly to the junction 296 .without passing through heat exchanger 287, entering the expander at a temperature of 3l5.7F, in which case the nitrogen and methane components may be liquefied in the expander. In either case, the stream from the junction 296 flows at a pressure of about 1,200 pounds per square inch, absolute, at substantially the 'flow rates and composition indicated in Table 24 here- I inbefore.

Turbo expander 298 is substantially similar in form to expander 239, described with reference to the sys- I tem of FIGS. 3A and 33 combined as 3C. In accordance with a variation of present practice, this may be connected in tandem to compressor 312 so that the enserves to refrigerate the feed stream, ultimately passing out through the conduit 19 at a pressure of about 890 pounds per square inch, absolute. The final tempera ture of the stream depends on whether or not it undergoes the reheat step through the heat exchanger prior to entering the 'turbo expander 298. Assuming the product stream has been reheated prior to expansion, which is the preferred case, the final temperature of the enriched product stream, after passing through column d of heat exchanger 287, is 19F in case A, and 94F in case B; The composition of the emerging enriched product stream is as indicated in Table 24 hereinbefore.

The residue liquid in the bottom of the helium flash drum 290 passes out through the conduit 301 under control of the valve 302, the latter being controlled electrically or pneumatically by the conventional liquidlevel control circuit 3020 to maintain the liquid level in the vessel 290. This liquid stream flows-out at a pressure of 1,200 pounds per square inch absolute and at a temperature 315.7F. The flow rate and composition are indicated on Table 25, below.

inster? H Liquid from Flash Drum Case A Case B Flow Rate (Std. Cubic ft./rnin.) [at F, 1 atm. pressure] 5,130 3,389 Composition (Mol Hydrogen 1.2253 0.843 8 Helium 1.2143 1.2211 Nitrogen 94.7107 95.91 12 Methane 2.8497 2.0239

305, similar to 262, FIG. 3A, which provides a surface for degassing the descending liquid and freeing dissolved helium vapors.

The liquid residue in the bottom of the container 304 is boiled slightly by means of a conventional bayonet heater 306 which is connected to a 2 kilowatt source of power 307. Conduit 308 in the dome takes off the vapor rising to the top of the vessel, the liquid portion being entrained in the stainless steel packing 305 in the body portion of the container.

The vapor rising from the conduit 308, has a pressure of about 20 pounds per square inch, absolute. The temperature, flow rate, and composition are indicated below in Table 26.

hine 26 Vapor from Helium Stripper into column c of heat exchanger 287 where it is heated up to a temperature of 32.8F, in case A, and 94F in case B, passing out through the conduit 311 and into the compressor 312 where the pressure is raised'from atmospheric pressure to about 1,205 pounds per square inch absolute, ultimately passing through the watercooled after cooler 313, to compensate for the heat of expansion. In one alternative, this recycle stream may be combined with waste nitrogen passing from conduit 17 through valve 17a. The compressed stream then passes into the junction 210 to merge with the stream for recycling through the system.

feed 

2. A process in accordance with claim 1 comprising three successive operations wherein: said natural gas contains between about 15 and 40 mol percent of helium, said crude helium product contains between about 60 and 80 mol percent of helium, said enriched helium product contains between about 85 and 97 mol percent of helium, and said grade A helium product has an impurity content which is less than about 30 parts per million.
 3. The process in accordance with claim 1 wherein in the second of said operations, the enriched helium vapor from said one flashing stage is passed through a reheating step prior to said work-expansion step for warming up said vapor to a temperature exceeding the condensation temperature of the components of said vapor by more than the expected temperature reduction during said work-expansion step whereby no liquid is formed in said vapor during said work-expansion step.
 4. A process in accordance with claim 1 wherein in the second of said operations said cooling is carried out in two steps: the first said step comprising a heat exchange with multiple streams, including returning enriched helium product and recycle streams, and the second said step comprising a subcooling step in a heat exchange with only the work-expanded enriched helium product stream.
 5. A process in accordance with the first of said operations set forth in claim 1 wherein said by-product condensed hydrocarbons are separated out as one or more streams employed to cool said feed gas stream, each of which hydrocarbon streams may optionally be returned for recycling with said partially helium vapor, wherein said by-product condensed hydrocarbons consist of commercial grade fuel having a heating capacity of between 850 and 950 British Thermal Units per cubic foot.
 6. A process in accordance with claim 1 wherein refrigeration for the cooling Steps in each of said operations is furnished entirely by condensate from the flashing stages and from work expansion in the said operation, with the exception of the final said operation wherein supplementary refrigeration for the cooling steps including refrigeration of said carbon desorbing means is furnished from an auxiliary nitrogen source.
 7. A process in accordance with claim 1 wherein condensate comprising waste nitrogen from said first and second operations is optionally returned with the recycle stream in each of said operations.
 8. A process in accordance with claim 6 wherein the liquid condensate from the additional stage of said second operation and from the later stages of said third operation is nitrogen having a purity in excess of 96 mol percent; and wherein said nitrogen is employed for reactivating (airpurifying) adsorbers in the final one of said operations.
 9. A process in accordance with claim 1 wherein in the final one of said operations said enriched helium feed stream is heated up to a temperature in excess of 200*F prior to dehydrogenation in the presence of a catalyst, the step of deriving fuel gas from the separated stream of condensed hydrocarbons in siad first operation for heating up said feed stream in the preliminary stages of said third operation during the initial period or when said feed stream is hydrogen deficient.
 10. A process for deriving crude helium from natural gas which comprises the steps of: compressing a feed stream comprising said natural gas to about 30 atmospheres pressure, cooling said compressed feed gas stream to below the condensation point of a major portion of hydrocarbons in said feed stream by heat exchange with returning crude helium product and condensate streams, separating out a first stream of condensed hydrocarbons from said feed stream in at least one flashing step and utilizing said condensed hydrocarbons for cooling said feed gas stream, subcooling the vapor from said flashing step to at least about the condensation point of nitrogen in a further heat exchange with returning crude vapor product and condensate streams, stripping the subcooled feed gas stream of helium by flashing in a plurality of successive stripping stages at progressively lower pressures to produce crude helium product vapor from the first of said flash stages and partially helium vapor from the remainder of said flash stages, separating out a stream of condensed hydrocarbons from the last of said successive stripping stages, returning said crude helium product vapor through said heat exchange steps for warming said crude helium vapor, and cooling said compressed feed gas stream, returning and recycling the partially helium vapor obtained from the remainder of said flashing stages, and vaporizing and utilizing the said streams of hydrocarbon condensate from said flashing and stripping stages to provide refrigeration for said heat exchange steps, said streams of returning crude helium, partial helium and hydrocarbon condensate providing adequate internal refrigeration for said crude helium derivation process without the use of an auxiliary refrigeration cycle.
 11. A process in accordance with claim 10 for deriving a crude product containing between 60 and 80 mol percent of helium from natural gas containing between 15 and 40 mol percent of helium wherein: said compressed feed stream is cooled to about -140*F by heat exchange with returning crude helium product and condensate streams, said first stream of condensed hydrocarbons is separated from said feed stream by a pair of successive flashing steps, the first at about 30 atmospheres pressure and the second at about 13.5 atmospheres pressure, the said stream from said second flashing stage is utilized for cooling said feed gas stream, the vapor from said first flashing step is subcooled to a temperature of -254*F in a further heaT exchange with returning crude vapor product and condensate streams, the subcooled feed gas stream is stripped of helium by flashing in a plurality of successive stages in which: the first of said stages is at a pressure of 30 atmospheres, the second of said stages which receives the liquid condensate from the first of said stages is at a pressure just in excess of 13 atmospheres, the third of said stages which receives the condensate from the second of said stages is at a pressure of just in excess of 5 atmospheres, and said second stream of condensed hydrocarbons is separated out from the last of said successive stripping stages at about 5.3 atmospheres pressure.
 12. A process for enriching a crude helium feed stream which comprises the steps of: compressing said feed stream of crude helium to about 80 atmospheres pressure, cooling said feed stream in a heat exchange with enriched helium vapor product, liquid condensate, and recycle streams to at least about the condensation temperature of nitrogen, directing the said feed stream through at least one flashing stage for separating out enriched helium vapor from liquid condensate, work-expanding the said enriched helium vapor from said one flashing stage, directing the work-expanded enriched helium vapor through at least one heat exchange step with said feed stream to provide an enriched helium product stream at a temperature above 0*F, directing the condensate from said one flashing stage through at least one additional flashing stage for stripping the helium from said condensate, directing the vapor product of said additional flashing stage through at least one heat exchange step for cooling said feed stream, subsequently recompressing said last-named vapor product for recycling with said feed stream, and utilizing the condensate from said additional flashing stage for refrigerating said feed stream.
 13. A process in accordance with claim 12 wherein the enriched helium vapor from said one flashing step is passed through a reheat step prior to said work-expansion step for warming up the said vapor to a temperature exceeding the condensation temperature of the components of said vapor by more than the expected reduction in temperature in said workexpansion process, whereby no liquid is formed in said vapor during said work-expansion step.
 14. A process in accordance with claim 12 wherein said cooling is carried out in two steps: the first said step comprising a heat exchange with multiple streams including returning product and recycle streams, and the second said step comprising a subcooling step in a heat exchange with only the work-expanded enriched helium product stream.
 15. In a process for enriching a crude helium feed stream containing between about 60 and 80 mol percent of helium to an enriched product containing between 85 and 97 mol percent helium which comprises the steps of: compressing said feed stream of crude helium to about 80 atmospheres pressure at near ambient temperature, cooling said feed stream in a heat exchange with enriched helium vapor product, liquid condensate, and recycle streams to at least about the condensation temperature of nitrogen, and directing said feed stream through one high pressure flashing stage for separating out enriched helium vapor from liquid condensate, and directing the condensate from said high pressure flashing stage comprising nearly 96 mol percent nitrogen and small amounts of hydrogen and methane through at least one additional low pressure flashing operation including a reboiling operation for stripping helium from said condensate: during said cooling step dividing said feed stream into two components, a major component comprising at least about 95 percent by volume of the flow, and a minor component comprising less than about 5 percent by volume of the flow, coolinG said major component in a heat exchange with returning product and waste streams to at least about the condensation temperature of nitrogen, partially cooling said minor component in a heat exchange with a returning recycle stream, and subsequently further cooling said minor component in a heat exchange with evaporating liquid condensate in said reboiling operation in said additional flashing stage to at least about the condensation temperature of liquid nitrogen, the two said cooled component streams being combined at about said last-named temperature and directed as a combined stream to said high pressure flashing stage in which said enriched helium vapor is separated out, reheating said enriched helium vapor from said high pressure flashing stage to a temperature at least above the boiling point of the highest boiling component thereof in a heat exchange within the major component of said feed stream for substantially eliminating liquid therefrom, subsequently work expanding said enriched helium vapor to about 60 atmospheres pressure at a temperature of about -320*F, directing said work-expanded enriched helium vapor through at least one heat exchange with the major component of said feed stream in which said enriched vapor is warmed with a slight reduction in pressure to provide a product having a near ambient temperature, directing the vapor product from said additional flashing operation, containing about 30 mol percent of helium, and a balance of nitrogen, hydrogen, and trace hydrocarbons through at least one heat exchange step with a component of said feed stream prior to passing for recompression and recycling in said system, utilizing the condensate consisting of more than 96 mol percent nitrogen derived from said additional flashing operation for refrigerating said feed stream, and optionally merging the said condensate with the vapor product from said additional flashing operation for recompression and recycling in said system.
 16. The combination in accordance with claim 15 wherein the level of condensate in said reboiler is maintained at a preselected level by syphoning the said condensate from the bottom of the reboiler through a syphon providing a liquid head slightly above the said preselected liquid level in said reboiler; and wherein the pressure at the head of said syphon is regulated in accordance with the output vapor pressure from said reboiler.
 17. A process for enriching a crude helium stream containing between 60 and 80 mol percent of helium to an enriched product containing between 85 and 97 mol percent of helium which comprises the steps of: compressing said crude helium feed stream to about 80 atmospheres pressure at near ambient temperature, cooling said crude helium feed stream in a heat exchange with returning enriched helium vapor product, liquid condensate and recycle streams to at least about the condensation temperature of nitrogen, subsequently directing said cooled feed stream through a high pressure flashing stage where enriched helium vapor which consists of at least 95 mol percent of the helium is separated from liquid condensate, reheating said vapor from said high pressure flashing stage to a temperature at least above the boiling point of the highest boiling component thereof, turbo-expanding said reheated enriched helium vapor to about 60 atmospheres pressure, heating said turbo-expanded enriched helium vapor in said heat exchange with said feed stream to provide an enriched helium product at near ambient temperature, further flashing the liquid condensate comprising about 95 mol percent nitrogen derived from said high pressure flashing stage in a helium stripper at about 1 1/2 atmospheres pressure for stripping the helium from said condensate, and passing the condensate from said further flashing stage consisting of about 97 mol percent nitrogen Through heat exchange means for cooling said feed stream and out to the atmosphere at near ambient temperature, passing the said stream of vapor derived from said helium stripper comprising about 30 mol percent helium in heat exchange for cooling said feed stream and warming said vapor to near ambient temperature at near atmospheric pressure, and subsequently recompressing said last-named vapor product for recycling with said feed stream.
 18. The process in accordance with claim 17 wherein said liquid condensate from said further flashing stage consisting of about 97 mol percent nitrogen is optionally combined with said stream of vapor derived from said helium stripper for recompression and recycling in said system.
 19. The process in accordance with claim 17 wherein: said feed stream is cooled to -316*F in at least two heat exchange steps, the first said step is a heat exchange with returning product and recycle streams, and the second said step is a heat exchange with an expanded returning product stream.
 20. A process for preparing grade A helium from an enriched helium feed stream containing 85 to 95 mol percent of helium comprising in combination the following steps: deriving said feed stream at about 60 atmospheres pressure and ambient temperature, heating said enriched helium feed stream to above 220*F prior to partly dehydrogenating said feed stream together with a recycle stream including at most about 20 mol percent oxygen in the presence of a catalyst to convert all but a small excess of the hydrogen in said stream to water vapor, passing said partly dehydrogenated stream through a bed containing a reducing agent for removing the remaining hydrogen from said stream, drying and compressing said dehydrogenated stream to 185 atmospheres, separating said compressed stream into two components, each of said components being cooled by heat exchange with returning product and recycle streams to about -280*F, alternately flashing and further cooling said compressed dehydrogenated helium stream through a plurality of flashing and cooling stages in heat exchange with boiling liquid nitrogen for condensing nitrogen and hydrocarbon impurities from said stream, said stages comprising: passing said partially cooled feed stream through a first high pressure flashing stage, deriving helium vapor between about 92 and 96 mol percent pure from said first flashing stage, cooling said helium vapor from said first flashing stage to about -315*F in a heat exchange with returning vapor and product streams, and a further heat exchange in boiling liquid nitrogen in a first liquid nitrogen stage, passing said cooled partially purified helium through a second high pressure flashing stage at about -315*F, deriving from said second flashing stage a helium vapor having a purity in excess of 98 mol percent, containing less than about 2 mol percent nitrogen impurity, cooling the helium vapor stream from said second flashing stage to a temperature of about -340*F in a heat exchange with reheating vapor from a third high pressure flashing stage and boiling liquid nitrogen in a second liquid nitrogen stage, passing said stream through said third high pressure flashing stage at a temperature of -340*F, deriving helium vapor from said third flashing stage which exceeds 99 mol percent purity containing less than one mol percent nitrogen, reheating the purified vapor from said third flashing stage up to a temperature of about -320*F in a heat exchange with cooling vapor from said second flashing stage, recooling said vapor with boiling liquid nitrogen in a repass through said first liquid nitrogen stage, directing said reheated vapor at a pressure of at least about 82 atmospheres through an on-cycle one of a plurality of vessels comprising carbon adsorbing means, where trace amounts of hydrogen, nitrogen, and hydrocarbons are adsorbed, said adsorbing means assuming on-cycle and off-cycle connections in alternation, deriving a product stream of nearly 100 mol percent pure helium from said carbon adsorbing means, passing said product stream through a heat exchange with feed streams being cooled wherein said product stream is warmed up to a temperature of about 80*F at a pressure of about 182 atmospheres, deriving condensates from said first high pressure flashing stage and flashing said condensates through a fourth flashing stage at 1 1/2 atmospheres pressure and -320*F, wherein the condensate from said fourth flashing stage includes in excess of 95 mol percent nitrogen, passing the condensate from said fourth flashing stage in heat exchange with said feed stream for cooling said feed stream and vaporizing and heating said condensate up to about 80*F prior to venting said vaporized condensate, deriving condensates from said second and third flashing stages containing in excess of 96 mol percent of nitrogen with more than 2 mol percent helium and less than 0.5 mol percent methane, directing the condensates from said second and third flashing stages to a fifth stage flash vessel employed as a helium stripper maintained at a pressure of about 1 1/2 atmospheres, returning the vapor from said helium stripper containing in excess of 20 mol percent of helium through heat exchange with said feed stream for recycling through said system, deriving the condensate from said helium stripper (fifth stage) including in excess of 99 mol percent of liquid nitrogen and less than 0.5 mol percent methane, and passing said condensate in heat exchange with feed streams undergoing cooling, deriving nitrogen from an ancillary off-site source at a pressure of about 41 atmospheres and a temperature above ambient, and liquefying and using said nitrogen stream for refrigerating the on-cycle one of said adsorbers, and for refrigerating the vapor streams from said first, second and third flashing stages.
 21. The process in accordance with claim 20 wherein the method of purging the carbon bed of an off-cycle one of said adsorbing vessels of impurities adsorbed during said on-cycle connection which comprises: deriving a small component of hot compressed feed stream prior to after cooling, passing said component through the carbon bed of said off-cycle vessel, and subsequently passing the purged gases into the stream under purification for at least a partial repass through said process for preparing grade A helium.
 22. In the process in accordance with claim 20 providing refrigerant for the refrigeration coil of the on-cycle vessel of said plurality, and the coils of said boiling liquid nitrogen stages by the steps of: deriving high pressure gaseous nitrogen from an off-cycle source at about 41 atmospheres pressure, cooling the said high pressure nitrogen streams in two components in heat exchange with returning low pressure nitrogen streams, the major said high pressure component being cooled in said heat exchange operation to about -170*F and subsequently work-expanded to a temperature of about -310*F at just above atmospheric pressure prior to returning in said heat exchange with said cooling high pressure streams, the minor said high pressure component being cooled to about -275*F in said heat exchange with returning low pressure streams, adiabatically expanding said cooled high pressure minor component to about atmospheric pressure and a temperature of about -310*F in a pressure-controlled valve, subsequently flashing said cooled minor component to separate the liquid from the vapor, the vapor from said Flashing step returning in said heat exchange operation and merging with other returning low pressure streams, and the liquid from said flashing step passing for evaporation in the refrigeration coils of said on-cycle carbon adsorber, and the coils of said boiling liquid nitrogen stages, the resultant nitrogen vapor being returned for heat exchange with said high pressure nitrogen streams prior to being optionally returned to said off-cycle nitrogen source for refrigeration in other parts of said system.
 23. A system for converting a feed stream comprising natural gas to grade A purity helium which comprises in combination: a first unit for converting a feed stream comprising natural gas to crude helium which comprises in combination: means for compressing said natural gas feed stream to about 30 atmospheres pressure, a first heat exchanger for cooling said natural gas feed stream in a heat exchange with returning product and recycle streams and condensed liquid streams, means for separating out the condensed hydrocarbons from said natural gas feed stream comprising a flash drum having a plurality of stages at progressively lower pressures, a second heat exchanger connected to receive vapor from the first flash stage of said plurality of flashing stages for subcooling said vapor in a heat exchange with returning product and recycle streams, means comprising a helium stripper having a first stage at high pressure, and a plurality of subsequent stages at progressively lower pressures for separating a major portion of the helium vapor from said subcooled vapor, means for deriving crude helium product vapor from said first stage of said helium stripper and for returning said crude product vapor through said heat exchangers to means for transferring said crude helium product to the second unit of said system, means for deriving recycle vapor including a substantial component of helium from said subsequent stages of said helium stripper and for returning said recycle vapor through said heat exchangers, means for compressing said recycle vapor and returning said vapor to said feed stream, means for deriving condensed hydrocarbons from said plurality of flashing stages and returning a stream of said condensed hydrocarbons through said first heat exchanger for refrigeration by vaporization, and to storage, and means for deriving a stream comprising a high percentage of condensed hydrocarbons from the stages of said helium stripper and returning said stream through said first and second heat exchangers for refrigerating said heat exchangers; a second unit for converting said feed stream comprising crude helium to enriched helium, which comprises in combination: means for deriving a crude helium feed stream compressed to a pressure of about 80 atmospheres, heat exchanger means for cooling said crude helium feed stream to a temperature below the condensation point of liquid nitrogen, helium separation means connected to receive the cooled crude helium feed stream from said heat exchanger means for separating out enriched helium vapor from said feed stream, work-expansion means connected to receive and workexpand the enriched helium vapor from said helium separator, a system of conduits connected to receive the workexpanded enriched helium vapor from said work expansion means and to direct said enriched helium vapor product to return through said heat exchanger means for cooling said crude helium feed stream, and means for transferring said enriched helium product to the third unit of said system, a conduit connected to the bottom of said helium separator for deriving liquid condensate therefrom, auxiliary separation means connected to receive the liquid condensate from said helium separator, means for deriving the partly helium vapor from said auxiliary separation means and returning said vapor through said heat exchanger means for cooling said crude helium feEd stream, compressing means connected to said heat exchanger means for compressing and returning said partly helium vapor to said crude helium feed stream for recycling in said system, and means for deriving the primarily liquid condensate from said auxiliary separation means and for directing said condensate to pass through said heat exchanger means for evaporation therein to cool said crude helium feed stream; and a third unit for converting a feed stream comprising enriched helium to helium of grade A purity, which comprises in combination: means for deriving an enriched helium feed stream compressed to a pressure of about 60 atmospheres, means comprising a first heat exchanger for heating said feed stream up to a temperature in excess of 220*F, a source of a stream containing about 20 mol percent of oxygen for combining with said helium enriched feed stream, means comprising a catalytic dehydrogenator connected to receive said enriched feed stream in combination with said oxygen-containing stream for converting a major portion of the hydrogen in said feed stream to water vapor, means for receiving the output of said dehydrogenator comprising a chemical hydrogen adsorber, said first heat exchanger connected to cool the output of said adsorber in a heat exchange with the enriched helium feed stream entering said dehydrogenator, means for drying said dehydrogenated stream, compressing means connected to compress said dried stream to about 185 atmospheres pressure, means comprising an aftercooler connected to said compressing means, a second and third heat exchanger connected in tandem to receive said compressed dehydrogenated enriched helium stream in two components and to cool said stream components to below the condensation temperature of liquid nitrogen in a heat exchange with returning purified helium product, recycle, and condensate streams, flashing means comprising a first stage flash drum, for flashing the recombined components of said cooled enriched compressed dehydrogenated helium stream through a plurality of stages to separate out higher boiling liquid condensates from the helium containing vapor in said stream, means for deriving the nearly purified helium vapor from said first stage flash drum and directing said helium vapor for a partial repass through said second and third heat exchangers, a first liquid nitrogen boiler connected to receive and further cool the merged streams derived from repass of said second and third heat exchangers, means comprising a second stage flash drum connected to receive the output from said first nitrogen boiler and to separate the partially purified helium vapor from the condensate in said stream, a fourth heat exchanger for receiving and slightly cooling the helium vapor from said second stage flash drum, a second liquid nitrogen boiler connected to receive the slightly cooled helium vapor from said fourth heat exchanger and to further cool said vapor to a temperature of about -340*F, a third stage flash drum including means for separating the liquid condensate from helium vapor at a temperature of about -340*F, means including said fourth heat exchanger for slightly reheating the output of said third stage flash drum, nitrogen adsorbing means comprising a plurality of vessels each equipped with a bed of comminuted carbon connectable in alternation in respective on-cycle and off-cycle positions wherein said on-cycle vessel is connected to receive the nearly purified vapor from said third stage flash drum and said liquid nitrogen boiler for adsorbing residual impurities in said vapor including nitrogen, means for deriving the helium product vapor of grade A purity from said nitrogen adsorber and directing said purified product vapor through said second and third heat exchangers in tandem to the output of said system, auxiliary to the principal purificatIon system, said fourth stage flash drum maintained at a pressure of slightly over one atmosphere and at a temperature not exceeding about -320*F for receiving and flashing the liquid condensate from said first stage flash drum, means for deriving liquid condensate containing in excess of about 95 mol percent of nitrogen from said fourth stage flash drum and passing said liquid condensate through said second heat exchanger means for evaporation and heat exchange cooling said compressed enriched helium feed stream, wherein said condensate is heated up to above ambient temperature, venting means connected to said second heat exchanger for venting said vaporized condensate from said
 24. The combination in accordance with claim 23 wherein said first unit is designed to convert a feed stream of natural gas containing between 15 and 40 mol percent of helium to crude helium containing between 60 and 80 mol percent of helium; wherein said second unit is designed to convert a feed stream of crude helium containing between 60 and 80 mol percent of helium and to enriched helium containing between 85 and 97 mol percent of helium, and wherein said third unit is designed to convert a feed stream of enriched helium containing between 85 and 97 mol percent of helium to helIum of grade A purity having an impurity content not exceeding about 30 parts per million.
 25. The combination in accordance with claim 23 wherein the stream of condensed hydrocarbons in said first unit has a heating capacity of between about 850 and 950 British Thermal Units per hour, and wherein in said third unit for preparing grade A helium, said means for heating said enriched helium feed stream to in excess of 220*F includes a heater for application to said enriched helium feed stream before said first heat exchanger is warmed up, said heater including means for deriving a fuel comprising at least a portion of the stream of said condensed hydrocarbons from said first unit.
 26. The combination in accordance with claim 23 wherein said source of a stream containing about 20 mol percent of oxygen includes adsorbing means for adsorbing water vapor and carbon dioxide from said stream, and means for reactivating said adsorbing means comprising a stream of waste nitrogen which is a by-product of said second or third units.
 27. The combination in accordance with claim 23 comprising means for optionally returning waste nitrogen from said first and second operations in combination with the recycle stream in each of said operations.
 28. A system for converting a feed stream comprising natural gas to crude helium without auxiliary means for providing internal refrigeration, which comprises, in combination: means for compressing said feed stream to about 30 atmospheres pressure, a first heat exchanger for cooling said feed stream in a heat exchange with returning product, recycle, and condensed liquid streams, means for separating out the condensed hydrocarbons from said feed stream comprising a flash drum having a plurality of stages at progressively lower pressures, a second heat exchanger connected to receive vapor from the first flash stage of said plurality of flashing stages for subcooling said vapor in a heat exchange with returning product and recycle streams, means comprising a helium stripper having a first stage at high pressure, and a plurality of subsequent stages at progressively lower pressures for separating a major portion of the helium vapor from said subcooled vapor, means for deriving crude helium vapor from said first stage of said helium stripper and for returning said vapor through said heat exchangers to storage, means for deriving recycle vapor including a substantial component of helium from said subsequent stages of said helium stripper and for returning said recycle vapor through said heat exchangers, means for compressing said recycle vapor and returning said vapor to said feed stream, means for deriving a first stream comprising hydrocarbon condensate from said plurality of flashing stages and returning said first stream of condensate through said first heat exchanger for refrigeration and to storage, and means for deriving a second stream of hydrocarbon condensate from the stages of said helium stripper and returning said second stream of condensate through said first and second heat exchangers for refrigerating said heat exchangers.
 29. A system for converting natural gas into crude helium in accordance with claim 28 which comprises means for optionally combining said first and second streams of hydrocarbon condensate in said first heat exchanger into a by-product stream consisting of commercial grade fuel having a heating capacity of between 850 and 950 British Thermal Units per cubic foot.
 30. A system for converting natural gas into crude helium in accordance with claim 29 which comprises means for optionally combining and returning one or both of said streams of hydrocarbon with said recycle vapor.
 31. A system in accordance with claim 28 for converting a feed stream comprising natural gas including between 15 and 40 mol percent of helium to crude helium having a purity of 60 to 80 moL percent wherein said flash drum has at least two stages, the first of said stages being maintained at a pressure of about 30 atmospheres and a temperature of about -148*F, and the second of said stages being maintained at a pressure slightly in excess of 13 atmospheres at a temperature below -169*F; and wherein said helium stripper comprises at least three stages, the first stage being maintained at a pressure of about 30 atmospheres and a temperature of about -258*F, the second said stage being maintained at a pressure slightly in excess of 13 atmospheres at said temperature, and the third said stage being maintained at a pressure slightly in excess of 5 atmospheres at a temperature of about -264*F.
 32. A system for converting a feed stream comprising crude helium to enriched helium which comprises in combination: means for deriving a crude helium feed stream compressed to a pressure of in excess of about 80 atmospheres, heat exchanger means for cooling said crude helium feed stream to a temperature below the condensation point of liquid nitrogen, means comprising a helium separator connected to receive the cooled crude helium feed stream from said heat exchanger means for separating out enriched helium vapor from said feed stream, work-expansion means connected to receive and work-expand the enriched helium vapor from said helium separator, a system of conduits connected to receive the work-expanded enriched helium vapor from said work expansion means and direct said enriched helium vapor to return through said heat-exchanger means for cooling said crude helium feed stream, a conduit connected to the bottom of said helium separator for deriving liquid condensate therefrom, auxiliary separation means connected to receive the liquid condensate from said helium separator, means for deriving the partly helium vapor from said auxiliary separation means and returning said vapor through said heat exchanger means for cooling said feed stream, compressing means connected to said heat exchanger means for compressing and returning said partly helium vapor to said feed stream for recycling in said system, and means for deriving said liquid condensate comprising primarily nitrogen from said auxiliary separation means and directing said condensate to pass through said heat exchanger means for evaporation therein to cool said crude helium feed stream.
 33. The combination in accordance with claim 32 which comprises means for optionally returning the evaporated condensate comprising primarily nitrogen from said suxiliary separation means through said compression means for recycling in said system.
 34. The combination in accordance with claim 32 wherein a reheat cycle is connected ahead of said work-expansion means, said reheat cycle including a portion of said heat exchanger means for receiving the enriched helium vapor from said helium separator and reheating said vapor to a temperature exceeding the condensation temperature of any of the components of said vapor by more than the expected reduction in temperature in said work-expansion means, whereby no liquid is formed in said work-expansion means.
 35. A system for converting a feed stream comprising crude helium having a purity of 60 to 80 mol percent to enriched helium having a purity of between 85 and 97 mol percent which comprises in combination: means for deriving a crude helium feed stream compressed to in excess of about 80 atmospheres at an initial temperature in excess of about 40*F, conduit means for dividing said compressed crude helium feed stream into two components, one said component comprising in excess of about 95 percent by volume and the other said component comprising less than about 5 percent by volume, heat exchanger means for cooling said crude helium feed Stream to a temperature below the condensation temperature of liquid nitrogen, said heat exchanger means comprising: a first heat exchanger connected to receive and cool said minor component in a heat exchange with a returning recycle stream, means connected in series with said first heat exchanger comprising a reboiler coil interposed in the bottom of a helium stripper, a second heat exchanger connected to receive and cool said major component in a heat exchange with returning enriched helium product and condensate streams, means for combining the respective two crude helium components from said reboiler coil and said second heat exchanger at a temperature of about -316*F, means comprising said helium separator connected to receive the combined cooled crude helium feed stream from said heat exchanger means for separating out enriched helium vapor from said crude feed stream, work-expansion means comprising a turbo-expander connected to receive the enriched helium vapor from said helium separator and to work expand said vapor, a system of conduits connected to receive the work-expanded enriched helium vapor from said work expansion means and direct said enriched helium vapor to return through said heat exchanger means for cooling said crude helium feed stream, a conduit connected to the bottom of said helium separator for deriving liquid condensate therefrom, auxiliary separation means connected to receive the liquid condensate from said helium separator, wherein said auxiliary separation means comprises: a first auxiliary flash drum maintained at about 2 atmospheres pressure, a second auxiliary flash drum maintained at slightly above atmospheric pressure and serving as said helium stripper connected to receive the liquid condensate from said first auxiliary flash drum for boiling in heat exchange with the cooled feed stream in said reboiler coil to separate out any vapor including helium vapor therefrom, means for deriving a partly helium vapor from said auxiliary flashing separation means comprising conduit means connected between the tops of said first and second auxiliary flash drums and said first heat exchanger for supplying refrigeration to said heat exchanger, compressing means connected to said heat exchanger means for compressing and returning said partly helium vapor to said feed stream for recycling in said system, and means for deriving said primarily liquid condensate comprising primarily nitrogen from said auxiliary separation means and directing said condensate to pass through said heat exchanger means for evaporation to cool said crude helium stream, said means comprising conduit means connected between the bottom of said second auxiliary flash drum and said second heat exchange means for supplying refrigeration thereto.
 36. The combination in accordance with claim 35 wherein means comprising a syphon is connected to the bottom of said second auxiliary flash drum serving as said helium stripper, said syphon constructed and arranged to maintain a preselected liquid level in said helium stripper-reboiler, a pressure-actuated valve being connected between the vapor output of said helium stripper and the head of said syphon for regulating the pressure in said syphon in accordance with the output vapor pressure of said helium stripper.
 37. The combination in accordance with claim 35 wherein: a three-way valve is connected to receive streams from the cold ends of each of said first and second heat exchangers and to supply a merged stream to the input of said helium separator, and means for controlling the ratio of the streams received from the path including said first heat exchanger and said reboiler coil, and the path including said second heat exchanger in accordance with the temperature differential between the warm ends of said heat exchangers.
 38. The combination in accordance with claim 35 wherein a reheat cycle is connected aHead of said turboexpander, said reheat cycle being connected through a portion of said second heat exchanger for receiving the enriched helium vapor from said helium separator and reheating said vapor to a temperature exceeding the condensation temperature of any of the components of said vapor by more than the expected reduction in temperature of said vapor in said turboexpander.
 39. A system in accordance with claim 38 for converting crude helium having a purity of 60 to 80 mol percent to enriched helium having a purity of between 85 and 97 mol percent: wherein said heat exchanger means is constructed to cool said feed stream to a temperature of about -315*F in heat exchange with returning enriched helium product, recycle, and condensate streams, wherein said work expansion means comprises a turboexpander for work expanding said enriched helium product to about 60 atmospheres pressure, wherein said auxiliary separation means comprises a single helium stripper connected to receive the condensate from said helium separator, said stripper maintained at an internal pressure of slightly above 5 atmospheres and including packing means for separating liquid from vapor in said stripper, said stripper including a bayonet heater connected to a source of energizing power for reboiling liquid condensate collected in the bottom of said stripper, and means for separately returning the liquid condensate and partially helium vapor from said helium stripper through said heat exchanger means, and for returning said partially helium vapor to said compressor for recycle.
 40. The combination in accordance with claim 35 wherein said heat exchanger means comprises a single heat exchanger for cooling said feed stream in heat exchange with enriched helium product vapor, partly helium vapor, and liquid condensate from said helium stripper, wherein the said single heat exchanger includes a reheat coil connected to receive and partly reheat said enriched product vapor from said helium separator ahead of said turboexpander.
 41. A system in accordance with claim 35 wherein said heat exchanger means comprises a first heat exchanger for cooling said crude helium feed stream in heat exchange with expanded enriched helium product vapor and a second heat exchanger interposed between said first heat exchanger and said helium separator in the path of said cooled feed stream for subcooling said crude helium feed stream in a heat exchange with enriched helium product from said turboexpander.
 42. A system for preparing grade A helium from an enriched helium feed stream which comprises in combination: means for deriving an enriched helium feed stream compressed to a pressure of about 60 atmospheres, means comprising a first heat exchanger for heating said feed stream up to a temperature in excess of 220*F, a source of a stream containing about 20 mol percent of oxygen for combining with said helium enriched feed stream, means comprising a catalytic dehydrogenator connected to receive said enriched feed stream in combination with said oxygen containing stream for converting a major portion of the hydrogen in said feed stream to water vapor, means for receiving the output of said dehydrogenator comprising a chemical hydrogen adsorber, said first heat exchanger connected to cool the output of said adsorber in a heat exchange with the enriched helium feed stream entering said dehydrogenator, means for drying said dehydrogenated stream, compressing means connected to compress said dried stream to about 185 atmospheres pressure, means comprising an aftercooler following said compressing means, a second and third heat exchanger connected in tandem to receive said compressed dehydrogenated enriched helium stream in two components and to cool said stream components to below the condensation temperature of liquid nitrogen in a heat exchange with returning purifiEd helium product, recycle, and condensate streams, flashing means, comprising a first stage flash drum, for flashing the recombined components of said cooled enriched compressed dehydrogenated helium stream through a plurality of stages to separate out higher boiling liquid condensates from the helium-containing vapor in said stream, means for deriving the nearly purified helium vapor from said first stage flash drum and directing said helium vapor for a partial repass through said second and third heat exchangers, a first liquid nitrogen boiler connected to receive and further cool the merged streams derived from repass of said second and third heat exchangers, means comprising a second stage flash drum connected to receive the output from said first nitrogen boiler and to separate the partially purified helium vapor from the condensate in said stream, a fourth heat exchanger for receiving and slightly cooling the helium vapor from said second stage flash drum, a second liquid nitrogen boiler connected to receive the slightly cooled helium vapor from said fourth heat exchanger, and to further cool said vapor to a temperature of about -340*F, a third stage flash drum including means for separating the liquid condensate from helium vapor at a temperature of about -340*F, means including said fourth heat exchanger for slightly reheating the output of said third stage flash drum, nitrogen adsorbing means comprising a plurality of vessels each equipped with a bed of comminuted carbon connectable in alternation in respective on-cycle and off-cycle positions, wherein said on-cycle vessel is connected to receive the nearly purified vapor from said third stage flash drum and said liquid nitrogen boiler for adsorbing residual impurities in said vapor including nitrogen, means for deriving the purified helium product vapor from said nitrogen adsorber and directing said purified product vapor through said second and third heat exchangers in tandem to the output of said system, auxiliary to the principal purification system, said fourth stage flash drum maintained at a pressure of slightly over one atmosphere at a temperature of about -320*F for receiving and flashing the liquid condensate from said first stage flash drum, means for deriving liquid condensate containing in excess of about 95 mol percent of nitrogen from said fourth stage flash drum and passing said liquid condensate through said second heat exchanger means for evaporation to cool said compressed enriched helium feed stream, wherein said condensate is heated up to near ambient temperature, venting means connected to said second heat exchanger for venting said vaporized condensate from said system, means for deriving the condensates from said second and third stage flash drums containing in excess of about 96 mol percent of nitrogen and more than 2 mol percent of helium, means including a fifth-stage vessel functioning as a helium stripper for receiving said condensates from said second and third flashing stages, said helium stripper maintained at slightly over one atmosphere pressure at a temperature of less than about -320*F for stripping the remaining helium from said condensates, means connected to said helium stripper for returning the partially helium vapor from said helium stripper through said second heat exchanger for recycling through said system, and means for deriving the condensate from said helium stripper consisting of about 99 mol percent of liquid nitrogen and passing said condensate through said third heat exchanger for evaporation to cool one component of said cooling compressed helium feed stream, wherein said condensate is heated up to near ambient temperature, means for deriving any condensate from said fourth stage flash drum consisting of at least about 95 mol percent of liquid nitrogen and such condensate from said heliuM stripper as is required for heat balance in said second heat exchanger, and passing said condensate through said second heat exchanger for evaporation and heat exchange with the other component of said cooling compressed helium feed stream, wherein said condensate is heated up to about ambient temperature, venting means connected to receive the evaporated condensate from said second heat exchanger for venting said last-named evaporated condensate consisting of nitrogen having a purity of at least about 95 mol percent, an off-site source of nitrogen maintained at a pressure of about 41 atmospheres, means comprising a nitrogen liquefaction circuit for deriving a stream of nitrogen gas from said off-site source at said last-named pressure at near ambient temperature and converting said stream to liquid nitrogen and means for directing the said liquefied nitrogen to the coil of said on-cycle adsorbing means for refrigerating said means at least during the on-cycle connection thereof, and to said liquid nitrogen boilers for refrigerating the partially purified helium stream, and means connected to receive the evaporated condensate from said third heat exchanger for returning at least a part of the evaporated condensate consisting of nitrogen having a purity of about 99 mol percent to said off-site nitrogen source to make up losses.
 43. In a system in accordance with claim 42 for preparing grade A helium having an impurity content not exceeding about 30 parts per million from an enriched helium feed stream containing between 85 and 97 mol percent helium, means for purging the carbon bed of an off-cycle one of said carbon adsorbing means which comprises in combination a purge connection to said compressing means ahead of said aftercooler for deriving from said compressing means a small component of hot compressed feed stream, a system of valves for alternatively connecting said purge connection to the off-cycle one of said carbon adsorbing means, and means simultaneously connectable to said off-cycle adsorbing means for venting the purged gases into said compressed feed stream for at least a partial repass through said system commencing just ahead of said second and third heat exchangers.
 44. In a system in accordance with claim 42 wherein said nitrogen liquefaction system comprises in combination: a heat exchanger connected to said off-site source to receive a high pressure stream of nitrogen gas from said off-site source, at a pressure of about 41 atmospheres at least at ambient temperature, and to cool said stream in two components in heat exchange with low pressure nitrogen streams returning through said heat exchanger, means comprising a turboexpansion device connected to receive the major component of said high pressure nitrogen stream after partial cooling in said heat exchanger to about -170*F, and to expand said stream to about atmospheric pressure, and to further cool said component to a temperature of about -310*F, conduit means for returning said cooled low pressure major stream through said heat exchanger for cooling said high pressure streams, means comprising a pressure-controlled expansion valve for receiving the minor high pressure component of said stream cooled to about -275*F at a pressure of about 40 atmospheres and expanding said component to a pressure just above atmospheric pressure at a temperature of about -310*F, a flash drum connected to said valve to receive said minor stream after expansion and separate the vapor phase from the liquid phase in said stream, conduit means connected between the upper portion of said flash drum and said conduit means for returning said major stream for returning the vapor portion of said minor component through said heat exchanger, conduit means connected between the lower end of said flash drum and the refrigeration coils of at least the on-Cycle one of said carbon adsorbers for supplying refrigerant to said coils, conduit means connected between the lower end of said flash drum and the coils of said liquid nitrogen boilers for supplying refrigerant to said boilers, conduit means connected to the refrigeration coils of said carbon adsorber and to the refrigeration coils of said nitrogen boilers for returning the evaporated nitrogen from said coils through said heat exchanger, and means for optionally returning said evaporated nitrogen to said off-cycle nitrogen source or to said system for recycle with the stream under purification. 